Is this shipping tax rate calculation approach correct?

Hello everyone,

While fetching orders from Shopify via the provided api I’ve fetched interesting order with shipping tax. Short example of it is here https://paste.xtrafrancyz.net/vOHWyLn9hD.groovy
It looks like shipping tax rate = 0.0783333 has been calculated like this:
price from shipping tax lines = 0.47 divided by shipping price = 6. The calculation on the numbers 0.47 / 6 = 0.0783333

  1. Is everything ok with such a calculation approach and is this not some bug? Because shipping tax rate = 0.0783333 is calculated and is not fixed as a rate.
  2. Are arbitrary rates normal for shipping or items? As I’m aware tax rates always are fixed and sometimes can be defined for some regions.
  3. Where can I get more details about such cases related to shipping tax rate calculation?

If I need to provide more technical details from my side please let me know.

Thanks in advance for your answers.
Best regards, Alexander